The present invention relates to a failure diagnosis apparatus for a throttle valve actuating device having an actuator for actuating a throttle valve provided in an intake system of an internal combustion engine, and more particularly to a failure diagnosis apparatus for a throttle valve actuating device including elastic members for maintaining an opening of the throttle valve at a predetermined retention opening when the throttle valve is not actuated by the actuator.
In a throttle valve actuating device that includes a motor for actuating a throttle valve and is configured so that the throttle valve is maintained at a fully closed position when a current is not supplied to the motor, a method for detecting a failure such that the throttle valve does not normally operate is disclosed in Japanese Patent Publication No. 2538731.
According to this method, it is determined that the throttle valve actuating device fails when the throttle valve opening detected by a throttle valve opening sensor is not in the vicinity of a full-closure opening in the condition where the current supply to the motor is stopped.
In this conventional method, the failure determination is performed in the condition where the current supply to the motor is stopped. In other words, the failure determination is performed in the condition where the throttle valve opening is not controlled. Accordingly, it is necessary to set a threshold for this determination in consideration of variations in characteristics of the throttle valve and the throttle valve opening sensor, so as to increase accuracy of the failure determination. As a result, every time a control unit for the throttle valve actuating device is started, a reference opening must be learned, which may cause a problem of an increase in calculation load on the control unit for performing the failure determination.
It is accordingly an object of the present invention to provide a failure diagnosis apparatus which can reduce the calculation load on the control unit and perform the failure determination with high accuracy by a relatively simple method.
To achieve the above object, the present invention provides a failure diagnosis apparatus for a throttle valve actuating device (10) having actuating means (6) for actuating a throttle valve (3) provided in an intake system (2) of an internal combustion engine (1) and biasing means (4, 5) for biasing the throttle valve (3) to a predetermined retention opening (THDEF). The failure diagnosis apparatus includes first control means, second control means, and determining means. The first control means performs a feedback control of the throttle valve (3) so that an opening (TH) of the throttle valve (3) coincide with a first predetermined opening (DCCMDMIN, DCCMDRTX). The second control means performs a feedback control of the throttle valve (3) so that the opening (TH) of the throttle valve (3) coincide with a second predetermined opening (DCCMDDFT, DCCMDRET) after the throttle valve (3) is controlled to the first predetermined opening (DCCMDMIN, DCCMDRTX) by the first control means. The determining means determines that the throttle valve actuating device (10) has failed when the time period (CDFTCHK, CRETCHK) during which the opening (TH) of the throttle valve (3) remains in a predetermined determination range (from (DCCMDDFTxe2x88x92DFTSPGOKL) to (DCCMDDFT+DFTSPGOKH), from (DCCMDRETxe2x88x92RETSPGOKL) to (DCCMDRET+RETSPGOKH)) including the second predetermined opening (DCCMDDFT, DCCMDRET), is shorter than a predetermined time period (CDFTCHKOK, CRETCHKOK) during an operation of the second control means.
With this configuration, the throttle valve is first controlled with the feedback control to the first predetermined opening, and is next controlled with feedback control to the second predetermined opening. When the time period during which the opening of the throttle valve remains in the predetermined determination range including the second predetermined opening is shorter than the predetermined time period during the execution of the feedback control to the second predetermined opening, it is determined that the throttle valve actuating device has failed. Thus, the failure determination is performed during the execution of the feedback control of the throttle valve opening. Accordingly, it is not necessary to learn the predetermined determination range, and the failure determination can be performed with high accuracy by a relatively simple method.
Preferably, the predetermined retention opening (THDEF) is an opening at which the engine is operable even when the actuating means (6) stops actuating the throttle valve(3).
With this configuration, the throttle valve opening is maintained at the predetermined retention opening at which the engine is operable even when the actuating means stops actuating the throttle valve. Accordingly, even when the throttle valve actuating device has failed, it is possible to obtain an engine output required for moving a vehicle driven by the engine to a place for repairing.
Preferably, the first predetermined opening is an opening (DCCMDMIN) at which the throttle valve (3) is substantially fully closed, and the second predetermined opening (DCCMDDFT) is less than the predetermined retention opening (THDEF) and greater than the first predetermined opening (DCCMDMIN).
With this configuration, the throttle valve is first controlled with the feedback control to the fully-closed opening, and is next controlled with the feedback control to the second predetermined opening which is less than the predetermined retention opening and greater than the fully-closed opening. In other words, the failure determination is performed while the throttle valve is being controlled with the feedback control in the valve opening direction from the fully-closed opening, so that it is possible to determine abnormality of the biasing means for biasing the throttle valve in the valve opening direction.
Preferably, the first predetermined opening is an opening (DCCMDRTX) which is greater than the predetermined retention opening (THDEF), and the second predetermined opening (DCCMDREY) is greater than the predetermined retention opening (THDEF) and less than the first predetermined opening (DCCMDRTX).
With this configuration, the throttle valve is first controlled with the feedback control to the first predetermined opening which is greater than the predetermined retention opening, and is next controlled with the feedback control to the second predetermined opening which is greater than the predetermined retention opening and less than the first predetermined opening. In other words, the failure determination is performed while the throttle valve is being controlled with the feedback control in the valve closing direction from the first predetermined opening which is greater than the predetermined retention opening, so that it is possible to determine abnormality of the biasing means for biasing the throttle valve in the valve closing direction.
Preferably, the second control means includes limiting means for limiting a control amount (DUT) to be supplied to the actuating means (6) when performing the feedback control to make the opening (TH) of the throttle valve (3) coincide with the second predetermined opening (DCCMDDFT, DCCMDRET).
With this configuration, the control amount to be supplied to the actuating means is limited when performing the feedback control of the throttle valve to the second predetermined opening. If the throttle valve actuating device is normal, the feedback control to the second predetermined opening can be performed even when the control amount is limited. However, if the throttle valve actuating device has failed, the feedback control to the second predetermined opening with a limited control amount cannot be completed, which makes it possible to detect the failure of the throttle valve actuating device.
Preferably, the limiting means limits the control amount (DUT) so that the throttle valve (3) can be controlled to the second predetermined opening (DCCMDDFT, DCCMDRET) when the biasing means (4, 5) is normal, while the throttle valve (3) cannot be controlled to the second predetermined opening (DCCMDDFT, DCCMDRET) when the biasing means (4, 5) is abnormal.